1. Field of the Invention
The present invention relates to a sense amplifier overdriving circuit and a semiconductor device using the same, and, more particularly, to a sense amplifier overdriving circuit which overdrives sense amplifiers at the level of an external voltage for a predetermined period to prevent the internal voltage of the sense amplifiers from being abruptly dropped during operation of the sense amplifiers in such a manner that the overdriving operation is carried out only for sense amplifiers belonging to a currently-activated cell block, and a semiconductor device using the sense amplifier overdriving circuit.
2. Description of the Related Art
Semiconductor memory devices, which are used for storage of information, have advanced toward low cost, reduced size, and large capacity, in accordance with the technical advances in computer systems and electronic communication fields. Also, the developments of such semiconductor memory devices have advanced toward inhibition of unnecessary current consumption because of increased demand for enhanced energy efficiency.
Generally, the cell array of a dynamic random access memory (DRAM) device to store data includes a number of cells each of which includes one n-channel metal oxide semiconductor (NMOS) transistor and one capacitor that are connected to word lines and bit lines connected in the form of a net.
Hereinafter, operation of such a general DRAM device will be described in brief.
When a row address strobe (RAS) signal /RAS, which is a main signal to activate the DRAM device, transits to an active state (low-level state), address signals are inputted to a row address buffer. In this state, a row decoding operation is carried out to decode row address signals output from the row address buffer, and thus, to output a row address for selecting one of the word lines in the cell array.
When data of each cell connected to the selected word line is applied to a pair of bit lines, namely, a bit line BL and a complementary bit line /BL, connected to the cell, a sense amplifier enabling signal is enabled, thereby activating a sense amplifier driving circuit for a cell block selected by the row address. In accordance with operation of the activated sense amplifier driving circuit, respective bias potentials of a sense amplifier associated with the sense amplifier driving circuit are transitioned to a core potential Vcore and a ground potential Vss, so that the sense amplifier is activated. When the sense amplifier is activated, the potential difference between the bit lines BL and /BL, which has been kept minute, is amplified. Subsequently, a column decoder, which is selected by a column address, turns on a column transfer transistor which serves to transfer the data on the bit line BL and the data on the bit line /BL to data bus lines DB and /DB, respectively. Accordingly, the data transferred to the bit line BL and the data transferred to the bit line /BL are sent to the data bus lines DB and /DB, respectively. Thus, the data is outputted to the outside of the DRAM device.
That is, the bit lines BL and /BL of each bit line pair is in a state of being precharged to ½ Vcc before the semiconductor memory device operates, namely, in the standby mode. When the bit lines BL and /BL receive data from the associated cell in accordance with operation of the semiconductor memory device, the potentials of the bit lines BL and /BL are varied to have minute differences. When the sense amplifier connected to the bit lines BL and /BL begins to operate in the above state, the potentials of the bit lines BL and /BL are varied to a core potential Vcore and a ground potential Vss, respectively. Namely, amplification of the data on the bit lines BL and /BL is carried out. The amplified data from the bit line BL and the amplified data from the bit line /BL are sent to the data bus lines DB and /DB in accordance with a column decoder output signal yi, respectively.
In the above-mentioned conventional semiconductor memory device, however, a large amount of current is abruptly consumed at the point of time when the sense amplifier begins to operate in accordance with reception of the internal voltage, namely, a core voltage, VCORE. As a result, there is a problem in that the internal voltage VCORE is abruptly dropped. In order to solve this problem, a method, in which the external and internal voltage terminals of the semiconductor memory device are short-circuited at the point of time when the sense amplifier operates such that an external voltage is supplied to the internal voltage terminal, has been widely used. This method is referred to as “sense amplifier overdriving”, and the circuit, which achieves such sense amplifier over driving, is referred to as a “sense amplifier overdriving circuit.” In conventional sense amplifier overdriving methods, however, an external voltage is applied to each cell block of a cell array irrespective of whether or not the cell block is in operation. As a result, the current consumption in execution of the sense amplifier overdriving operation is unnecessarily excessive, thereby causing degradation in the energy efficiency of the semiconductor device (as seen in FIG. 4).